U.S. patent application number 13/123745 was filed with the patent office on 2011-11-03 for bonding device, ultrasonic transducer, and bonding method.
This patent application is currently assigned to HESSE & KNIPPS GMBH. Invention is credited to Michael Broekelmann, Hans-Juergen Hesse, Piotr Vasiljev, Joerg Wallaschek.
Application Number | 20110266329 13/123745 |
Document ID | / |
Family ID | 41821369 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110266329 |
Kind Code |
A1 |
Hesse; Hans-Juergen ; et
al. |
November 3, 2011 |
BONDING DEVICE, ULTRASONIC TRANSDUCER, AND BONDING METHOD
Abstract
A bonding device, particularly for producing bond connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as electrical
circuits, wherein the bonding device comprises a bonding head (2)
which can be rotated about a geometric axis of rotation (D), in
particular a vertical axis, and on which a bonding tool (5) and an
ultrasonic transducer (35) are disposed for ultrasonic vibration
excitation of the bonding tool (5). It is proposed that the main
direction of extension (36) of the ultrasonic transducer (35)
and/or the direction of extension thereof in the direction of the
axis of the minimum moment of inertia extends parallel to the
geometric axis of rotation (D) of the bonding head (2). The
invention further relates to a bonding device or an ultrasonic
transducer.
Inventors: |
Hesse; Hans-Juergen;
(Paderborn, DE) ; Wallaschek; Joerg; (Paderborn,
DE) ; Broekelmann; Michael; (Delbrueck, DE) ;
Vasiljev; Piotr; (Vilnius, LT) |
Assignee: |
HESSE & KNIPPS GMBH
Paderborn
DE
|
Family ID: |
41821369 |
Appl. No.: |
13/123745 |
Filed: |
October 7, 2009 |
PCT Filed: |
October 7, 2009 |
PCT NO: |
PCT/EP09/63000 |
371 Date: |
April 12, 2011 |
Current U.S.
Class: |
228/110.1 ;
228/1.1 |
Current CPC
Class: |
H01L 2924/01068
20130101; H01L 2924/01005 20130101; H01L 24/78 20130101; H01L
2924/00014 20130101; H01L 2924/01013 20130101; H01L 2924/01074
20130101; H01L 2224/45124 20130101; H01L 2224/45014 20130101; H01L
2224/45144 20130101; H01L 2224/78313 20130101; H01L 2224/45144
20130101; H01L 2924/00014 20130101; B23K 20/106 20130101; H01L
2924/01047 20130101; H01L 2924/01061 20130101; H01L 2924/01082
20130101; H01L 2224/45124 20130101; H01L 2924/014 20130101; B23K
20/002 20130101; H01L 24/85 20130101; H01L 2924/01015 20130101;
H01L 2924/07802 20130101; H01L 2924/07802 20130101; H01L 2924/00015
20130101; H01L 2224/48 20130101; H01L 2924/00015 20130101; H01L
2924/00 20130101; B23K 2101/42 20180801; H01L 21/67138 20130101;
H01L 2924/01033 20130101; H01L 2224/85205 20130101; H01L 2924/01079
20130101 |
Class at
Publication: |
228/110.1 ;
228/1.1 |
International
Class: |
B23K 20/10 20060101
B23K020/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2008 |
DE |
10 2008 037 450.4 |
Jan 6, 2009 |
DE |
10 2009 003 312.2 |
Claims
1. A bonding device, particularly for producing bond connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as, in particular,
electrical circuits, wherein the bonding device comprises a bonding
head (2) which can be rotated about a geometric axis of rotation
(D), on which a bonding tool (5) and an ultrasonic transducer (35)
for ultrasonic vibration excitation of the bonding tool are
disposed, wherein, the main direction of extension (36) of the
ultrasonic transducer (35) and/or it's direction of extension in
direction of the axis of the minimum mass moment of inertia extends
in parallel to the geometrical axis of rotation (D) of the bonding
head (2).
2. An ultrasonic transducer, particularly for a bonding device for
the ultrasonic oscillation excitation of the bonding tool of the
bonding device, wherein the ultrasonic transducer comprises at
least one oscillation exciter and the oscillation exciter comprises
at least one piezo element, and wherein an ultrasonic energy
source, particularly a voltage source is utilized to apply an
alternating electrical voltage to the piezo element, wherein the
ultrasonic energy source, particularly the voltage source (42),
particularly its frequency, is matched to or adjustable such that
during operation, particularly when the alternating voltage is
applied, the main direction of deformation of the oscillation
exciter (37) and/or the main direction of deformation of the piezo
element (38) extends transverse to the polarization direction (P)
of the piezo element (38).
3. A bonding device, particularly for producing bond connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as, in particular,
electrical circuits, wherein the bonding device (1) comprises a
bonding head (2) which comprises a bonding tool (5) and an
ultrasonic transducer (35) according to claim 2.
4. An ultrasonic transducer for the ultrasonic oscillation
excitation of a bonding tool, wherein the ultrasonic transducer
comprises at least two spaced apart oscillation exciters connected
to a tool holder and which comprises at least one ultrasonic energy
source for powering of the oscillation exciters, particularly at
least one voltage source to apply alternating electrical voltage to
the oscillation exciter, wherein one or more ultrasonic energy
sources, in particular the voltage source (42) or the voltage
sources, preferably the frequency and/or the phase position are
matched or tunable to the oscillation exciter (35) and the bonding
tool (5) in such manner that during operation the main directions
of deformation of the two oscillation exciters (37) are parallel or
mainly parallel to each other and the resulting deformations, that
change in time, of the two oscillation exciters in the main
directions of deformation are phase shifted with respect to each
other, preferably by half a period.
5. A bonding device, particularly for producing bonding connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as, in particular,
electrical circuits, wherein the bonding device comprises a bonding
head on which a bonding tool, particularly a wedge, is mounted in a
tool receptacle, wherein an ultrasonic transducer according to
claim 4 is provided on the bonding head of the bonding device.
6. The bonding device according to claim 1, wherein the geometrical
longitudinal center line (S) of the ultrasonic transducer (35)
extends parallel to the geometrical rotational axis (D) of the
bonding head (2), particularly on the axis of rotation (D) or in
close proximity hereto, and/or parallel to the longitudinal center
line (W) of the bonding tool (5), particularly on the longitudinal
center line (W) or in close proximity hereto.
7. The bonding device according claim 1, wherein the ultrasonic
transducer (35) comprises at least one oscillation exciter (37),
and each oscillation exciter (37) comprises at least one piezo
element (38), wherein each piezo element (38) features a main
direction of extension (41) that extends parallel to the
geometrical rotational axis (D) of the bonding (2) head.
8. The bonding device according to claim 3, wherein the ultrasonic
energy source, particularly the voltage source (42), particularly
its voltage frequency, is matched or adjustable such that when
applying the alternating voltage, the main direction of deformation
of the oscillation exciter (37) and/or the piezo element (38)
extends at least mainly into the main direction of extension (41)
of the piezo element (38).
9. The bonding device according to claim 5, wherein the design of
the bonding head (2) components that can be excited to oscillate by
the ultrasonic transducer (35) and the alternating voltage,
particularly its frequency, is adjusted or adjustable to each other
such that the pivot point (P) of the tool holder (6) is located at
a nodal point of the bonding tool (5).
10. The bonding device according to claim 1, wherein the frequency
of the ultrasonic energy source, particularly the voltage frequency
at the voltage source is chosen or adjustable such that it at least
approximately equals a resonant frequency, particularly the lowest
resonant frequency of the oscillating subassembly with applied
alternating voltage, which includes the ultrasonic transducer (35),
the tool holder (6), and the bonding tool (5).
11. The bonding device according to claim 1, wherein one or several
piezo elements (38) each has the shape of a rectangular delimited
plate, wherein the polarization direction (P) of each piezo element
(38) is oriented lateral with respect to its plate plane.
12. The bonding device according to claim 1, wherein the ultrasonic
transducer (35) comprises at least two oscillation exciters (37)
arranged parallel to each other, wherein each oscillation exciter
(37) comprises a piezo element holder (16) and two similar piezo
elements (38), that are mounted planar to two surfaces (39, 40) of
the piezo element holder (16) that are parallel to, turned away
from and opposite to each other, particularly with the planar
surfaces bonded to them.
13. The bonding device according to claim 1, wherein the
polarization directions (P) of piezo elements (38) that are
constituents of the same oscillation exciter are opposing each
other with respect to their direction.
14. The bonding device according to claim 12, wherein the
polarization directions (P) of the two piezo elements (38) that are
attached to one of the two piezo element holders (16) are oriented
away from the surface of the piezo element holder (16), and that
the polarization direction (P) of the two piezo elements (38),
which are attached to the other of the two piezo element holders
(16) are oriented towards the surface of the piezo element holder
(16).
15. The bonding device according to claim 12, wherein the piezo
elements (38) are connect to the ultrasonic energy source,
particularly to the voltage source (42), on their free surface
facing away from the piezo element holder (16), and that the piezo
element holders (16) are grounded.
16. The bonding device according to claim 3, wherein the ultrasonic
energy source, particularly the voltage source (42) is adjusted to
supply an alternating voltage which is in phase for all piezo
elements (38), particularly by wiring the connecting wires (43, 45)
of all piezo elements (38) in parallel.
17. The bonding device according to claim 3, wherein the bonding
tool comprises a geometrical longitudinal tool axis (W) that
extends parallel to the main direction of extension (41) of the
piezo elements (38) and/or extends along the geometrical axis of
rotation (D) of the bonding head (2).
18. The bonding device according to claim 12, wherein the two piezo
element holders (16) are constituents of a shared single piece
transducer body (15), at which particularly also the tool holder
(6) is implemented as a single piece.
19. The bonding device according to claim 18, wherein the
transducer body (15) comprises a holding fork (19), with holder
arms (20) that on their its longitudinal ends (21) each engage
respectively one piezo element holder (16) in its longitudinal
center area.
20. An ultrasonic transducer, comprising at least one transducer
body (15) and at least one oscillation exciting element (55) that
for the transmission of the oscillations produced by the
oscillation exciting element itself is connected with the
transducer body (15) by suitable means, wherein the ultrasonic
transducer (35) particularly with the at its tool holder (6)
mounted bonding tool (5) exhibits an oscillation mode, comprising a
waveform which produces a rotational oscillating movement with
respect to at least one axis of rotation (A) in the mounting point
of the bonding tool or produces a combined oscillatory excitation
for rotation and translation.
21. The ultrasonic transducer according to claim 20, wherein the
oscillation excitation element (55) is mounted to the transducer
body (15) by force closure and/or form closure and/or material
continuity (bonding, brazing, welding etc.).
22. The ultrasonic transducer according to claim 20, wherein the
oscillating rotational movement is oriented about a geometrical
axis of rotation (A) perpendicular or at least in general
perpendicular to the longitudinal axis (W) of the bonding tool
(5).
23. The ultrasonic transducer according to claim 20, wherein a
geometrical reference plane (E) passes through the geometrical
longitudinal axis (W) of the bonding tool (5) or a hereto parallel
geometrical line and through said rotational axis, that the at
least one oscillation excitation element (55) is located spaced
apart and to the side of reference plane (E), and that the force
exerted from the oscillation excitation element (55) onto the
transducer body (15) acts into or predominantly into the direction
of the longitudinal axis (W) of the bonding tool (5).
24. The ultrasonic transducer according to claim 23, wherein at
least two with respect to the reference plane (E) sideways spaced
apart oscillation excitation elements (55) are provided, that are
arranged opposite of each other with respect to the reference plane
(E).
25. The ultrasonic transducer according to claim 20, wherein it
comprises one or more ultrasonic energy sources, in particular one
or more voltage sources, to supply energy to the oscillation
exciter elements (55), and that are connected to the oscillation
exciter elements (55) such that these, particularly oscillation
exciter elements (55) that are arranged on the same or on different
sides of the reference plane with reference to each other, perform
oscillations with a phase shift of 180.degree. to each other.
26. The ultrasonic transducer according to claim 23, wherein a
minimum of two oscillation excitation elements (55) are arranged on
each side of the reference plane (E), wherein oscillation
excitation elements (55) provided on both sides of the reference
plane (E) are arranged in pairs opposite to each other, wherein on
the same side of the reference plane (E) neighboring oscillation
excitation elements (55) are connected with the energy source or
the energy sources such that they perform oscillations with a phase
shift of 180.degree. to each other, and wherein oscillation
excitation elements (55) that are arranged in pairs and with
respect to the reference plane (E) opposite to each other are
connected with the energy source or energy sources such that they
perform oscillations with a phase shift to 180.degree. to each
other.
27. The ultrasonic transducer according to claim 23, wherein that
respectively at least two excitation elements (55) on the same side
of the reference plane (E) are arranged one behind the other in the
direction of the geometrical longitudinal axis (W) of the bonding
tool (5).
28. The ultrasonic transducer according to claim 20, wherein the
transducer body (15) comprises only one oscillation excitation
element carrier (57) and that the oscillation excitation elements
(55), particularly all oscillation excitation elements (55), when
constituting an oscillation exciter are provided on two opposing
and opposite sides facing surfaces (39, 40) of the oscillation
excitation elements carrier (57), wherein the oscillation
excitation element carrier (57) exhibits at least substantially the
form of a rectangular cuboid or of a rectangular plate.
29. The ultrasonic transducer according to claim 20, wherein as
oscillation exciter elements (55) respectively at least one piezo
element (38) is provided and that the transducer body (15)
comprises only one piezo element holder (16), holding all piezo
elements, which at least fundamentally features the form of a
rectangular cuboid or a rectangular plate.
30. A process for producing bond connections particularly between
electrical conductors made of wire material or strip material and
contact points of substrates such as particularly electrical
circuits, with the following process steps: providing a bonding
tool, providing an ultrasonic transducer for the ultrasonic
excitation of the bonding tool, wherein the ultrasonic transducer
comprises at least one oscillation exciter and the oscillation
exciter comprises at least one piezo element, providing an
ultrasonic energy source to drive the piezo element preferably a
voltage source to apply an alternating electrical voltage to the
piezo element, and oscillation excitation of the bonding tool while
pushing against the electrical conductor to be bonded by means of a
bonding tool onto a contact point, wherein for the oscillation
excitation of the bonding tool (5) the ultrasonic energy source,
particularly the voltage source (42), particularly its ultrasonic
frequency, is chosen or adjusted such that during operation the
geometrical main deformation line (49) of the oscillation exciter
(37) and/or the main deformation line (50) of the piezo element
(38) is oriented transversal to the polarization direction (P) of
the piezo element (38).
31. A process for producing bond connections particularly between
electrical conductors made of wire material or strip material and
contact points of substrates such as particularly electrical
circuits, with the following process steps: Providing a bonding
tool and an ultrasonic transducer for the ultrasonic excitation of
the bonding tool, oscillation excitation of the bonding tool while
pushing against the electrical conductor to be bonded by means of a
bonding tool onto a contact point, wherein for its oscillation
excitation an oscillating torsional moment (M) is applied to the
bonding tool (5) at the tool holder (6), with a geometrical axis of
rotation (A) of the torsional moment (M) that extends transversal
to the tools longitudinal axis (W) or that introduces an
oscillating torsional moment (M) and an oscillating translatory
excitation into the bonding tool (5) for its oscillatory excitation
at the tool holder (6).
32. A process according to claim 31, wherein the oscillating
torsional moment (M) is introduced into the bonding tool (5) at the
location of a nodal point of the bonding tool (5).
33. A process according to claim 30, wherein a bonding device (1)
according to one or several of the previous claims is utilized.
Description
[0001] The invention relates to a bonding device, particularly for
producing bond connections between electrical conductors made of
wire material or strip material and contact points of substrates
such as, in particular, electrical circuits, wherein the bonding
device comprises a bonding head which can be rotated about a
geometric axis of rotation, in particular a vertical axis, and on
which a bonding tool and an ultrasonic transducer are disposed for
ultrasonic vibration excitation of the bonding tool.
[0002] As is known such bonding devices perform in a way that by
means of a bonding tool, that in a common embodiment could be a
so-called wedge, an area of an electrical conductor that is to be
bonded, e.g. an Aluminum or Gold wire, is pushed against the
targeted contact point of a substrate, e.g. an electrical circuit,
with a defined compressive force, while the bonding tool is
performing ultrasonic oscillations perpendicular to the direction
of the compressive force and transmits those oscillations into the
conductor until a permanent so-called bond connection is
established between the conductor and the contact point. For the
excitation of the ultrasonic oscillation of the bonding tool
so-called ultrasonic transducers are utilized, that typically use
stacks of plate-shaped piezo elements as oscillation drivers. The
piezo elements are usually connected to an alternating voltage such
that the piezo elements perform consecutive elongations and
contractions predominantly perpendicular to the planes of the
plates and therefore in the longitudinal direction of the piezo
element stack. These periodical alternations of length usually
excite the tool holder of the bonding tool to perform longitudinal
mechanical oscillations in the direction of the periodical
alternations of length. As tool holder often a conically reducing
horn that elongates into the same direction is utilized with the
bonding tool attached to its tip, e.g. by means of a clamping
screw, such that the longitudinal axis of the tool is perpendicular
to the longitudinal axis of the transducer, i.e. perpendicular to
the direction of the oscillation. As a result the tip of the tool
also performs an oscillating movement transverse to the tool's
longitudinal axis that is utilized to produce a bond connection.
Bonding devices with ultrasonic transducers provide numerous
advantages and are used in a multitude of applications. Frequently
there is a requirement to produce a number of bond connections
within a small area, wherein the so-called bonding head, i.e. the
subassembly of the bonding device containing the bonding tool and
the ultrasonic transducer (as well as usually a wire guide and as
the case my be for so-called thick wire bonders a cutting tool) are
mounted, needs to perform quick rotary motions around a vertically
oriented geometrical axis of rotation. The fact that a conventional
ultrasonic transducer equipped with a bonding head due to its
function and hence its design exhibits a large mass moment of
inertia is regarded as a constraining factor, hampering the
rotation of the bonding head and accordingly requires large rotary
drives.
[0003] In this context it is the objective of the invention to
further develop a bonding device of the aforementioned kind such
that particularly the disadvantages described above are largely
avoided.
[0004] The objective is accomplished by the invention firstly and
fundamentally by an embodiment wherein the main direction of
extension of the ultrasonic transducer and/or the direction of
extension thereof in the direction of the axis of the minimum
moment of inertia (with or without lateral distance) extends
parallel to the geometric axis of rotation of the bonding head. The
aforementioned main direction is the extension direction of the
ultrasonic transducer, wherein it exhibits its largest physical
dimension in comparison to its extension direction. Also the
aforementioned axis of rotation of the bonding head is primarily a
geometrical, i.e. not necessarily a constructional axis. With the
chosen solution according to the invention a reduction of the mass
moment of inertia with respect to the geometrical bond head axis of
rotation is achieved, in comparison to conventional bonding devices
with a main direction of extension of the ultrasonic transducer
perpendicular to the geometrical axis of rotation of the bonding
head.
[0005] Therefore faster rotations of the bonding head with respect
to its perpendicular geometric axis of rotation are possible
respectively smaller drive systems are necessary for the rotational
drives in comparison.
[0006] A second embodiment according to the invention features an
ultrasonic transducer, particularly for a bonding device for the
ultrasonic oscillation excitation of the bonding tool of the
bonding device, wherein the ultrasonic transducer comprises at
least one oscillation exciter and the oscillation exciter comprises
at least one piezo element, and wherein an ultrasonic energy
source, particularly a voltage source is utilized to apply an
alternating electrical voltage to the piezo element.
[0007] Based on the aforementioned state of the art the objective
of the invention is to further develop such ultrasonic transducer
to achieve advantages with respect to manufacturing technology
and/or its application.
[0008] This objective is accomplished by the invention firstly and
fundamentally by an embodiment wherein the ultrasonic energy
source, particularly the voltage source, preferably its frequency,
and in particular its voltage frequency, is matched to or
adjustable such that during operation, particularly when an
alternating voltage is applied, the main direction of deformation
of the oscillation exciter and/or the main direction of deformation
of the piezo element extends laterally respectively perpendicularly
to the polarization direction of the piezo element. This embodiment
represents a fundamental departure from transducer designs
according to the state of the art, wherein the main direction of
deformation of the oscillation exciter (e.g. a stack of piezo
element plates), respectively the main direction of deformation of
the piezo elements themselves, is arranged parallel to the main
deformation direction of the piezo elements. At this the main
deformation direction is defined as the spatial direction in which
compared to other directions the largest deformations occur (i.e.
contractions and elongations) caused by the applied alternating
electrical voltage. The polarization direction is a property of the
piezo element, a directional orientation achieved by a forced
alignment of dipoles in an electrical filed during the
manufacturing process of piezo elements and for the most part
remains after the manufacturing process is completed (so-called
remanent polarization). Through Application of an alternating
voltage to the piezo element it generally experiences alternating
contractions and elongations in all spatial directions, in which
the respective magnitude and amount in the different spatial
directions usually varies. The invention is based on the knowledge
that specific alternating voltages exist, that in a case by case
specifically allocated single spatial direction (e.g. geometrical
axis of the body) result in an elongation of a larger magnitude
compared to other spatial directions, in which these frequencies
are also dependent on the form and the dimensions of the piezo
element as well as the case may be dependent on adjacent
respectively resonant components. According to the invention the
proposed embodiments provide at defined voltages comparatively high
field strengths particularly with the usage of plate shaped
respectively thin piezo elements with a polarization direction
extending perpendicular respectively lateral to the plate plane and
thus create transmittable forces through changes in physical shape.
Additional advantages are the achievement of increasing degrees of
freedom for designing the transducers and the possibility of a
simplified assembly of the piezo elements. The invention includes a
bonding device particularly for producing bonding connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as, in particular,
electrical circuits, wherein the bonding device comprises a bonding
head comprising a bonding tool and an ultrasonic transducer as
described above.
[0009] A third embodiment of the invention comprises an ultrasonic
transducer for the ultrasonic oscillation excitation of a bonding
tool wherein the ultrasonic transducer comprises at least two
interspaced oscillation exciters connected to a tool holder and
which comprises at least one ultrasonic energy source for the
supply of the oscillation exciters, particularly at least one
voltage source to apply alternating electrical voltage to the
oscillation exciter.
[0010] Based on the aforementioned the objective of the invention
is to provide an advantageous embodiment of such bonding
device.
[0011] According to the invention the objective is firstly and
fundamentally accomplished by an embodiment wherein one or more
ultrasonic energy sources, in particular the voltage source or the
voltage sources, preferably the frequency and/or the phase position
e.g. of the alternating voltage or alternating voltages thereof,
are chosen or adjustable to the construction of the oscillation
exciter in such manner that in operation, particularly with applied
alternating voltage, the main directions of deformation of the two
oscillation exciters are parallel or mainly parallel to each other
and the deformations that change in time of the two oscillation
exciters are phase shifted with respect to each other, preferably
by half a period, i.e. phase shifted by 180.degree.. The term
period in this context is used in place or as an equivalent to the
term phase length, and a phase shift of 180.degree. (antiphase)
represents half a phase length forward in a phase shift. With
respect to its third embodiment the invention also comprises a
bonding device particularly for producing bonding connections
between electrical conductors made of wire material or strip
material and contact points of substrates such as, in particular,
electrical circuits, wherein the bonding device comprises a bonding
head comprising a bonding tool, preferably a wedge, that is held by
a tool holder, and an ultrasonic transducer according to the
invention as described above. By utilizing several, preferably two,
piezo elements that are interspaced with respect to each other,
attached to the tool holder, and that perform different
time-deformation-characteristics, the tool holder performs an
oscillating rotational movement and transmits this movement onto
the end of the preferably elongated bonding tool held by the tool
holder. By means of the periodically changing rotational angle of
the tool holder respectively by the oscillating torsional moment
transmitted to the bonding tool, the bonding tool is excited to
perform transversal oscillations, i.e. oscillations perpendicular
or lateral to its linear expansion respectively its main direction
of extension. But this oscillation also called flexural oscillation
or transverse oscillation is in contrast to the state of the art
not excited at the position of the so-called antinode, but
preferably at the position of the so-called node of the frequency
dependent mode of oscillation. The transverse oscillation is
transmitted to the entire bonding tool and causes in connection
with an appropriate design respectively configuration of the
bonding tool that also the bonding tool tip performs oscillations
transversal to the longitudinal direction of the bonding tool, that
can be transmitted to an electrical conductor for the production of
a bond connection by pressing the bonding tool against said
conductor.
[0012] It is understood that in the context of the invention also
combinations of the characteristics of each two or all of the three
aforementioned embodiments of the invention are possible. In
principle all known piezo element types for piezo actuators could
be used as piezo elements at which the use of piezo-electrical
ceramics or piezo-electric crystals is preferred.
[0013] In particular in connection with the first embodiment of the
invention it is preferred that the geometrical longitudinal center
line of the ultrasonic transducer is oriented parallel to the
geometrical rotational axis of the bonding head and/or parallel to
the longitudinal center line of the bonding tool. Thus the moment
of inertia with respect to the bonding head rotational axis can be
reduced. There is also the possibility that the ultrasonic
transducer comprises at least one oscillation exciter, preferably
two oscillation exciters oriented parallel to each other, wherein
each oscillation exciter comprises at least one piezo element,
preferably two piezo elements, wherein each piezo element features
a main direction of extension that extends parallel to the
geometrical rotational axis of the bonding head. The term main
direction of extension implies that the dimension of the piezo
element in this direction is larger than in any other
directions.
[0014] In particular in connection with the second embodiment of
the invention it is preferred that the ultrasonic energy sources,
particularly the voltage source, preferably its voltage frequency,
is chosen or adjustable such that when applying the alternating
voltage, the main direction of deformation of the oscillation
exciter and/or the main direction of deformation of the piezo
element respectively the piezo elements extends along the main
direction of extension of the piezo element respectively the piezo
elements.
[0015] In particular in connection with the third embodiment of the
invention it is preferred that the design of the bonding head
components that can be excited by the ultrasonic transducer and the
alternating voltage, particularly its frequency, is chosen or
adjustable to each other such that the pivot point and particularly
the instantaneous center of rotation of the tool holder is located
at a node of the bonding tool.
[0016] In respect to the aforementioned embodiments of the
invention there is also the possibility that the frequency at the
ultrasonic energy source, preferably the voltage frequency at the
voltage source is chosen or adjustable such that it exactly or
approximately equals a resonant frequency, preferably the lowest
respectively the first resonant frequency, i.e. the first
eigenmode, of the with applied alternating voltage oscillating
subassembly, which includes the ultrasonic transducer, the tool
holder, and the bonding tool. Preferably the oscillating system
with the bonding tool can be excited to oscillations with its first
eigenfrequency and thus in its according first eigenform, but
oscillation excitation for e.g. the second or third etc.
eigenfrequency/eigenform would also be possible. In another
advantageous embodiment of the invention one or several piezo
elements each in the shape of a rectangular delimited plate,
wherein the edge length of the rectangular contour is larger than
the thickness of the plate and wherein the polarization direction
of each piezo element with respect to its plate plane is oriented
lateral respectively perpendicular.
[0017] For the introduction of an oscillating torsional moment into
the tool holder respectively into the bonding tool it is preferred
that the ultrasonic transducer comprises at least two oscillation
exciters arranged parallel to each other, wherein each oscillation
exciter comprises a piezo element holder and two similar piezo
elements, that are mounted planar to two surfaces of the piezo
element holder that are parallel to, turned away from and opposite
to each other, preferably with the planar surfaces glued to them.
Thereby and in connection with the chosen frequency of the
alternating voltage it can be achieved, that practically only the
elongation change of the piezo elements in their main direction of
extension is utilized for the oscillation excitation of the bonding
tool. By means of the planar attachment of the piezo elements also
the piezo holder element, which is preferably made from metal like
e.g. steel or titanium, is deformed accordingly. Thus each
oscillation exciter comprises a sandwich-like arrangement of a
central piezo element holder between two opposing piezo elements.
In connection with this configuration and the above mentioned
parallel arrangement of two such oscillating exciters it is
preferred that the polarization direction of piezo elements, which
are constituents of the same oscillation exciter, are opposing each
other with respect to their direction, thus quasi have opposite
leading signs. In this context it is also preferred that the
polarization direction of the two piezo elements that are attached
to one of the two piezo element holders is oriented orthogonally
away from the surface of the piezo element holder, and that the
polarization direction of the two piezo elements, which are
attached to the other of the two piezo element holders are oriented
orthogonally towards the surface of the piezo element holder. With
the above mentioned embodiments the desired different and
particularly opposing changes in length of the two oscillation
exciters can be realized with a particularly simple electrical
circuitry, wherein all piezo elements are connected to the same
respectively identical, thus also in-phase, alternating voltage and
the piezo element carriers are e.g. grounded. In particular this
provides the possibility to easily connect the piezo elements to a
free surface, facing away from the piezo element holder, to the
ultrasonic source, particularly to the voltage source e.g. by means
of soldering joints. Thus an ultrasonic energy source respectively
voltage course can the utilized, which provides only a single
alternating voltage e.g. in the form u(t)=U cos(.omega.t), and
which is applied to all piezo elements, e.g. by wiring the
connecting wires to all piezo elements in parallel. Another
advantageous embodiment with respect to the previously described
mode of operation is an arrangement where the geometrical
longitudinal axis of the bonding tool extends parallel to the main
direction of extension of the piezo elements and/or along the
geometrical axis of rotation of the bonding head. A preferred space
saving and stable embodiment comprises two piezo element holders
that are constituents of the shared single piece transducer body,
at which preferably also the tool holder for holding the bonding
tool is implemented as a single piece. On that note it is also
preferred that the transducer body integrally comprises a holding
fork, with holder arms that on its longitudinal end connect to each
one piezo element holder in its longitudinal center area.
[0018] In another embodiment of the invention an ultrasonic
transducer comprises at least one transducer body and at least one
oscillation exciting element that for the transmission of the
oscillations produced by the oscillation exciting element itself is
connected with the transducer body by suitable means, and it
proposes for the further advantageous development, that the
ultrasonic transducer preferably with the at its tool holder
mounted bonding tool comprises an oscillation mode, comprising a
waveform which produces a rotational oscillating movement with
respect to at least one axis of rotation in the mounting point of
the bonding tool. Alternatively said waveform in the mounting point
of the bonding tool may produce a combined oscillatory excitation
for rotation and translation. In a preferred embodiment of the
invention the oscillation excitation element is mounted to the
transducer body by force closure and/or form closure and/or
material continuity (bonding, brazing, welding etc.). It is also
preferred that the oscillating rotational movement is oriented with
respect to at least one to the longitudinal axis of the bonding
tool perpendicular or at least in general perpendicular imaginary
respectively geometrical axis of rotation. In further detail a
possible embodiment allows to span a hypothetical respectively
geometrical reference plane through the geometrical longitudinal
axis of the bonding tool or a hereto parallel geometrical line and
through said rotational axis, that the at least one oscillation
excitation element is located interspaced to the side and that the
force exerted from the oscillation excitation element onto the
transducer body acts into or predominantly into the direction
respectively parallel to the (imaginary extended) longitudinal axis
of the bonding tool. It is regarded as advantageous that at least
two with respect to the reference plane sideways interspaced
oscillation excitation elements are provided, that are arranged
opposite of each other with respect to the reference plane. In
another embodiment one or several ultrasonic energy sources,
preferably one or several voltage sources or current sources, are
provided for the energy supply of the oscillation excitation
elements, which are connected to the oscillation excitation
elements such that they perform oscillations that are phase shifted
by 180.degree..
[0019] In a preferred embodiment a minimum of two oscillation
excitation elements are arranged on each side of the reference
plane, wherein on both respectively on different sides of the
reference plane oscillation excitation elements are arranged in
pairs opposite to each other, wherein on the same side of the
reference plane neighboring oscillation excitation elements are
connected with the energy source or the energy sources such that
they perform oscillations with a phase shift of 180.degree. to each
other, and wherein oscillation excitation elements that are
arranged in pairs and with respect to the reference plane opposite
to each other are connected with the oscillation energy source or
oscillation energy sources such that they perform oscillations with
a phase shift to 180.degree. to each other. A compact advantageous
embodiment according to the invention particularly with respect to
a minimum mass moment of inertia with respect to the tool's
longitudinal axis is achieved with each at least two oscillation
excitation elements that are arranged one behind the other on the
same side of the reference plane in the direction of the
geometrical longitudinal axis of the bonding tool. This provides
the opportunity that the transducer body comprises only one
oscillation excitation element carrier and that the oscillation
excitation elements, preferably all oscillation excitation
elements, by configuring only a single oscillation exciter, are
located at two opposing, opposite sides facing surfaces of the
oscillation excitation elements carrier, wherein the oscillation
excitation element carrier exhibits at least substantially the form
of a rectangular cuboid or of a rectangular plate. In so far such
ultrasonic transducer is of a fundamentally different construction
compared to the previously described ultrasonic transducer with two
parallel to each other arranged oscillation exciters, but also
allows the introduction of an oscillatory torsional moment into the
bonding tool at its tool holder. In one embodiment the oscillation
exciter element is at least one piezo element such that the
transducer body comprises only one piezo element holder, holding
all piezo elements, which at least fundamentally features the form
of a rectangular cuboid or a rectangular plate.
[0020] From the above it becomes clear that the bonding device
according to the invention and its ultrasonic transducer
fundamentally deviate from the state of the art. Known transducers
usually used in ultrasonic welding are excited by one oscillation
generator to perform longitudinal oscillations, and transmit those
oscillations to a tool that is arranged perpendicular to the
direction of oscillation exciting it to perform flexural
oscillations. The invention in contrast targets a new design
wherein the orthogonal alignment of the tool to the transducer is
no longer necessary. Thus an improved construction with respect to
the mass moment of inertia and the physical volume of the apparatus
is achievable. In addition the manufacturing cost of the
transducers may be reduced by using simplified body geometries
(e.g. plates, plates with simple geometry) and by simplifying the
assembly of actuators respectively oscillation excitation elements
at the transducer. According to the embodiments of the invention
already described above the invention proposes that the main
direction of extension, i.e. the direction of the axis of the
minimum moment of inertia of the transducer, and of the tool is
identical. The transducer is excited to oscillations by oscillation
exciters respectively oscillation excitation elements, such that a
wave form develops at the operating frequency, that performs a
fundamentally rotational movement at the mounting point of the tool
and thus excites the tool in a node of its waveform to perform a
torsional oscillation. In an embodiment according to the invention
it is proposed that the transducer respectively transducer body
consists fundamentally of two coupled areas of a preferably plate
shaped body of arbitrary shape and as the case may be variable
(particularly in direction of the extension staggered) thickness
and excited by means of oscillation exciters respectively
oscillation excitation elements to perform longitudinal
oscillations, wherein the tool oscillates in the plane of the plate
shaped body. Preferably at least two actuators (oscillation
excitation elements) are mounted planar in the left or right area
on opposing outer surfaces of the transducer that are parallel to
the main direction of extension. Preferably the actuators are
mounted e.g. by bonding, but fundamentally all connections by force
closure, form closure and material continuity are possible
alternatively or in combination. The driving of actuators opposing
each other is preferably in phase. In one embodiment according to
the invention at least four actuators (oscillation excitation
elements) are mounted to two opposing outer surfaces of the two
coupled areas that extend parallel to the main direction of
extension. Within one area the actuators are again preferably
driven in phase, whereas the two areas are driven in antiphase
(phase is preferably 180.degree.).
[0021] With regard to the direction of the main direction of
extension and the aforementioned design this embodiment can be
categorized as a vertical transducer, featuring two coupling
areas.
[0022] Another embodiment according to the invention described
above features a transducer consisting of a plate shaped body that
is excited to oscillations by the oscillation exciter respectively
the oscillation excitation elements that are mounted on two outer
surfaces opposing each other and parallel to the transversal axis
of the transducer. The tool oscillates, in contrast to the
transducer consisting of two coupled partial bodies described
above, perpendicular to the plane of the plate shaped body. This
provides the opportunity to mount two actuators (oscillation
excitation elements) on the outer surfaces in the upper half of the
body and drive them in antiphase. One embodiment according to the
invention comprises four actuators (oscillation excitation
elements) mounted on the transducer, particularly two actuators on
each side and one each in the upper and lower half. The actuators
located on one side are preferably driven in antiphase. Hence the
actuators located diagonally opposing each other are driven in
phase. With respect to orientation and construction this embodiment
can be categorized as a single-piece body vertical transducer.
[0023] The invention provides for other embodiment comprising
combinations of a vertical transducer with two coupled areas and
the single-piece body vertical transducer. These combinations
enable the bonding tool in the mounting plane to not only oscillate
on a straight line but also on a circular path and/or to perform an
additional movement component perpendicular to the mounting
plane.
[0024] The invention also relates to a process for producing bond
connections preferably, i.e. not necessarily (other work pieces
i.e. plastic parts or other parts that could be welded by
ultrasound), between electrical conductors made of wire material or
strip material and contact points of substrates such as electrical
circuits, with the following process steps: Providing a bonding
tool, providing an ultrasonic transducer for the ultrasonic
excitation of the bonding tool, wherein the ultrasonic transducer
comprises at least one oscillation exciter and the oscillation
exciter comprises at least one piezo element, providing of an
ultrasonic energy source to drive the piezo element preferably a
voltage source to connect an alternating electrical voltage to the
piezo element, and oscillation excitation of the bonding tool while
pushing against the electrical conductor to be bonded by means of a
bonding tool onto a contact point.
[0025] Wit respect to the statements above it is the objective of
the invention to further develop advantageous embodiments of such
process for producing bond connections.
[0026] The objective is accomplished by the invention firstly and
fundamentally in connection with an embodiment wherein the
oscillation excitation of the bonding tool the ultrasonic energy
source, preferably the voltage source, preferably its ultrasonic
frequency, is chosen or adjusted such that during operation,
preferably with connecting to the alternating voltage, the main
direction of deformation of the oscillation exciter and/or the main
direction of deformation of the piezo element is oriented
transversal to the polarization direction of the piezo element.
[0027] The effects and advantages of this embodiment are referenced
above particularly in the explanations pertaining to the second
embodiment according to the invention.
[0028] The invention also relates to a process for producing bond
connections preferably between electrical conductors made of wire
material or strip material and contact points of substrates such as
electrical circuits, with the following process steps: Providing a
bonding tool and an ultrasonic transducer for the ultrasonic
excitation of the bonding tool and oscillation excitation of the
bonding tool while pushing against the electrical conductor to be
bonded by means of a bonding tool onto a contact point.
[0029] For the advantageous further development of such process the
invention proposes, that for its oscillation excitation an
oscillating torsional moment is applied to the bonding tool at the
tool holder, wherein the geometrical axis of rotation of the
torsional moment is oriented transversal to the tool's longitudinal
axis. Alternatively an advantageous further development of the
process according to the invention is that for its oscillation
excitation an oscillating torsional moment and an oscillating
translatory excitation is applied to the bonding tool at the tool
holder. In order to hold the bonding tool at the bonding device
respectively at the bonding head a tool holder holds the bonding
tool, preferably at its upper end. The effects and advantages of
this embodiment are referenced above particularly in the
explanations pertaining to the third embodiment according to the
invention. Preferably the process may be performed such that the
oscillating torsional moment is applied at the location of a node
of the bonding tool.
[0030] From the above it can be concluded that for the energy
supply of the oscillation exciter or the oscillation exciters
preferably but not necessarily a voltage source can be chosen.
Alternatively e.g. one or several current sources or other types of
energy sources (e.g. a magnetic energy source) may serve as energy
source for the generation of ultrasonic oscillation (i.e. as
ultrasonic energy source). In the context of the different
embodiments according to the invention the term oscillation exciter
is defined in general as a holder with at least two attached
oscillation exciter elements, i.e. with at least one actuator,
wherein the actuator can generally be based on a piezo-electrical
working principle (if implemented as a piezo element) or on a
magnetostrictive working principle.
[0031] The aforementioned processes according to the invention
preferably comprise an ultrasonic transducer respectively a bonding
device that exhibit one or several of the aforementioned and/or
subsequently described attributes.
[0032] In the following preferred embodiments of the invention will
be explained in more detail with reference to the illustrations
below. They show:
[0033] FIG. 1 a side view of a preferable embodiment of a bonding
head of a bonding device according of the invention;
[0034] FIG. 2 a magnified perspective view of the transducer shown
in FIG. 1;
[0035] FIG. 3 a side view of the ultrasonic transducer in viewing
direction III according to FIG. 2;
[0036] FIG. 4 a magnified cross sectional view of the ultrasonic
transducer along intersecting line IV-IV according to FIG. 3;
[0037] FIG. 5 a perspective view of the transducer body of the
ultrasonic transducer shown in FIG. 2
[0038] FIG. 6 a side view of the transducer body in viewing
direction VI according to FIG. 5 with a partial cross sectional
view at its lower end;
[0039] FIG. 7 a side view similar to FIG. 3, which shows exemplary
and schematically simplified areas of piezo elements with
deformations of various magnitudes;
[0040] FIG. 8 an example of a preferred holder of the ultrasonic
transducer for the attachment of the bonding head, as an
alternative embodiment to FIG. 1;
[0041] FIG. 9 a perspective view of an ultrasonic transducer
according to the invention with an inserted bonding tool according
to a further preferred embodiment;
[0042] FIG. 10 a cross sectional view along sectional plane Xa in
FIG. 9 in slightly smaller scale and
[0043] FIG. 10b a cross sectional view according to FIG. 10 wherein
a momentary waveform is indicated in a simplified schematic manner
by means of a dashed winding line.
[0044] With respect to FIGS. 1 through 6 a preferred embodiment of
a bonding device according to the invention and a process for
producing bond connections according to the invention is described,
wherein FIG. 1 shows the bonding device 1 only in the area of the
bonding head and the FIGS. 2 through 6 depict magnified views of
components of the bonding head 2. In a way not depicted here in
detail the bonding head 2 is mounted at the underside of a pulley 3
which is attached rotatable to the bonding device 1 around the
vertical oriented axis of rotation D. To perform a rotational
movement in this embodiment a partially shown toothed belt 4 that
engages with the teeth on the outer perimeter of a toothed pulley 3
may by means of a driven pulley it is wound around and not shown
here be moved a desired distance depending on the angle of
rotation. In addition drive systems may be provided to move the
entire bonding head 2 sideways in varying directions of a plane
perpendicular to the axis of rotation D. The bonding head 2
comprises an elongated bonding tool 5 that extends along a center
longitudinal axis W. At its upper longitudinal end it is inserted
with its shaft into a tool holder 6 into a likewise vertical bore 7
of according diameter (compare FIG. 6) and in there secured with a
clamp screw. At the lower longitudinal end the bonding tool 5
comprises a tool tip 9 that may push an electrical conductor, made
e.g. of wire material or strip material, with its lower face in a
known manner against a contact point of the substrate selected for
a bond connection, preferably a contact of an electrical circuit.
In order to provide the bonding location with a wire or strip
conductor the bonding device comprises a wire feed device 10 with a
guiding grove 11 at is lower end that is open to the side. In order
to steady the electrical conductor at defined points in time during
the bonding process and to be able to exert a tension on the
electrical conductor the bonding device comprises a clamp device
12, with two clamp legs 13 overlapping each other in the viewing
direction of FIG. 1, with their unoccupied ends located between the
tool tip 9 and the lower end of the wire feed device 10. The
generally known functionality of the wire feeding device and the
clamp device does not need to be explained here in detail. Both
components are adjustable in position and may be locked into a
desired position with respect to the pulley 3 respectively a stiff
holding arm attached at it with suitable means. The tool holder 6
is formed as a single piece to the lower end of the transducer body
15 shown in detail in FIGS. 5 and 6. The transducer body 15 made in
a plate-like form from an electrically conductive material (e.g.
steel) incidentally comprises two each rectangular delimited piezo
element holders 16 with a main direction of extension 17 extending
parallel to the geometrical axis of rotation D and the coinciding
or just minimally interspaced tool axis W. In each case in the
approximate area of the middle lower edge a connecting web 18
emanates from each piezo element holder, with each lower end of
which the two piezo element holders 16 are attached sideways
interspaced to each other (i.e. interspaced to each other
transversal to the axis of rotation D) to the upper side of the
tool holder 6. In addition the transducer body 16 comprises a
retaining fork 19 to hold the piezo element carriers 16 at the
bonding head 2. For this purpose two retaining arms 20 of the
retaining fork 19 contact each one piezo element holder 16 in its
longitudinal center area (with respect to the extension
respectively the dimension in the main direction of extension 17)
as a single piece at its lower longitudinal end 21. In the same
height the piezo element holders 16 that extend parallel to the
main direction of extension 17 are connected by means of a material
bridge 22. Apart from that the two piezo element holders 16 are
interspaced from each other with narrow slots 23, 24 and from the
retaining fork 19 by means of narrow slots 25, 26. In its upper
area the retaining fork 19 comprises through holes 27, to mount to
the transducer body 15 by means of screws 28 firmly to a plate 29.
The plate 29 is bolted with screws 30 to a frame section 31 that is
like the retaining arm 20 a component of the, to the underside of
the pulley 3 mounted, assembly frame 32. In FIG. 1 this frame in
depicted by a dashed line where it is covered by other components.
As depicted the assembly frame 32 comprises four sections 33 with a
comparatively reduced frame cross section exhibiting a
comparatively lower stiffness and that due to their flexibility
serve as solid state pivots. The with respect to FIG. 1 left edge
of the assembly frame 32 is like the retaining arm 20 rigidly
mounted to the pulley 3, whereas the frame section 31 to the right
in viewing direction due to the solid state pivots by a force F
that may be performed by an actuator, that is not shown, on the
frame section 34, may be deflected relative hereto for a certain
distance downwards to e.g. press the bonding tool 5 downwards onto
the bonding point. When the force F is removed the frame section 31
will elastically return to its rest position.
[0045] The FIGS. 2 through 4 show the transducer body 15 of the
ultrasonic transducer 35, as a component of the bonding head which
is shown in FIG. 1, with the bonding tool 5 inserted in its tool
holder 6. From FIGS. 1 and 3 e.g. it is evident that the main
direction of extension 36 of the ultrasonic transducer 35 may
extend parallel to the geometrical axis of rotation D of the
bonding head, which is coinciding with or just minimally
interspaced from the tool axis W of the bonding tool. Based on the
mainly symmetrical construction of the ultrasonic transducer 35, as
chosen in the example, its longitudinal axis of symmetry S, apart
from a small sideways displacement (compare .DELTA.X in FIG. 3),
also coincides with the geometrical axis D and W. The ultrasonic
transducer 35 that is shown magnified in FIGS. 2 through 4
comprises two neighboring oscillation exciters 37 oriented parallel
to each other. Each oscillation exciter 37 comprises one of the two
piezo element holders 16 as well as each two plate shaped, in their
main direction of extension (compare FIG. 3) rectangular delimited
piezo elements 38, from which the two corresponding piezo elements
that are each assigned to one oscillation exciters are bonded
planar onto the two opposing and parallel surfaces 39, 40 that are
facing away from each other, of the according piezo element holder
16 across the entire contact surface. FIGS. 2 and 3 show that in
this contact plane (i.e. parallel to the drawing plane of FIG. 3)
the delimitation respectively the shape of the piezo element holder
16 and of the piezo elements bonded thereon is identical, wherein
an accurately fitting and aligned bonding is present. From this
results that also the main direction of extension 41 of the piezo
elements 38 is oriented parallel to the geometrical axis of
rotation D of the bonding head 2. The chosen piezo elements can be
described as plate shaped because their dimension in the main plane
of extension, which is in parallel to the drawing plane of FIG. 3,
is larger that the thickness of the hereto perpendicular and
parallel to the drawing plane of FIG. 4 extending plane. In FIG. 4
the polarization direction of each piezo element is given and
depicted with arrows that are marked with the reference sign P. As
can be seen the polarization direction P of each piezo element 38
extends perpendicular to its plate plane. Also shown is that at
each pair of piezo elements 38, that belongs to the same
oscillation exciter, the polarization directions are oriented in
opposing directions with respect to each other. In further detail
of the embodiment shown in FIG. 4 the polarization directions P of
the piezo elements 38 of the, with respect to the viewing
direction, left oscillation exciter 37 extend perpendicular away
from the contact planes 39, 40, i.e. to the outside. In contrast
hereto the polarization directions P of the piezo elements 38 of
the oscillation exciter located to the right with respect to the
viewing direction are oriented each perpendicular in direction of
the according contact pane 39, 40, i.e. to the inside. The
ultrasonic transducer in the shown example is connected to a
voltage source 42 by attaching two electrical conductors 43 coming
from said voltage source that are connected in parallel and that
are attached at their ends by means of solder joints 44 to two
piezo elements opposing each other on the same (located on the
right in FIG. 4) piezo element holder 16. The symbol shown in FIG.
4 denotes that the voltage source 42 is an alternating voltage
source. Alternatively other ultrasonic energy sources (i.e. energy
sources for the generation of ultrasound), e.g. an alternating
current source may be utilized. By means of additional electrical
conductors 45 and their solder joints 44 pairs of piezo element
holders 38, which are bonded onto the neighboring piezo element
holders within the same plane, are connected electrically
conducting. In the example selected here also the respective bonded
joints between the piezo elements 38 and the piezo element holders
16 are manufactured electrically conductive, alternatively an
electrically not conducting bonded joint would also be possible.
The piezo element holders 16 are, as labeled by the reference
numerals 46, each (or together) grounded. Thus the same alternating
voltage with respect to magnitude and phasing is connected to each
of the four piezo elements 38 perpendicular to their plate plane,
when the voltage source 42 is turned on.
[0046] While FIG. 3 shows the ultrasonic transducer 35 and the
bonding tool 5 mounted therein with the voltage source 42 turned
off, FIG. 7 for comparison depicts schematically simplified and
exemplary the deformations of the oscillation exciters, the tool
holder 6, and the bonding tool 5 caused by the piezo electrical
effect with the voltage source turned on at a defined point in
time, i.e. during application of an alternating electrical voltage
with an exemplary frequency and amplitude chosen for the
calculations. For simplification the small deformations that also
occur in the area of the retaining fork 19 are not shown. Shown is
the overall deformation of a so-called main mode, wherein for the
purpose of the calculation the surface of the piezo elements 38 was
segmented into fields 47, delimited by grids. From the diagram-like
illustration it can be seen that the relative positional deviation
is smallest along an approximately central zone, connecting the
longitudinal ends 21 of the two retaining arms 20, and largest at
the two longitudinal ends of the piezo elements. In comparison with
FIG. 3 it can be clearly seen that the piezo elements 18 to the
left, with respect to the viewing direction, with the piezo element
carrier located in between, i.e. the oscillation exciter 37 located
left with respect to the viewing direction, undergoes a contraction
respectively linear shortening in the assigned main direction of
extension 17 respectively 41, by the applied alternating voltage
during the considered point in time in comparison to the idle state
with no voltage applied (see FIG. 3), while the neighboring
Oscillation exciter 37 to the right, including its two piezo
elements 38 and its piezo element holder 16, undergoes a linear
expansion at this point and in time in this direction. Despite the
electrical voltage being identical at all piezo elements at any
given point in time the two pairs perform oscillating deformation
oscillations that are shifted by half a phase length with respect
to each other caused by the different polarization directions as
described above. The numeral values assigned to the different
hatching styles show as comparative values the according relative
position deviation of the areas compared to the idle state with no
voltage applied shown in FIG. 3. Due to the opposing changes in
length of the two parallel oscillation exciters 37 the tool holder
48 is, compared to the idle state with no voltage applied as shown
in FIG. 3, lifted at its left longitudinal end and lowered at its
right longitudinal end, such that with respect to the pivot point
P.sub.M a torsion results in direction of the arrow 48. The pivot
point P.sub.M is located at the upper longitudinal end of the
bonding tool 5 that is attached to the tool holder, wherein the
geometrical axis of rotation of the torsion extends through the
point P.sub.M perpendicular to the drawing plane of FIG. 7 and in
so far also perpendicular to the longitudinal extension of the
bonding tool 5. Although all four piezo elements 38 are connected
to the same voltage the desired opposing change in length at the
two oscillation exciters 37 is achieved, because the polarization
direction P of the piezo elements 38 is oriented in opposing
directions between the two oscillation exciters 37. Because the
magnitude and leading sign of the alternating voltage, whose
frequency is in the ultrasonic range, thus the momentary magnitude,
constantly changes, which also results in a change in length of the
oscillation exciters 37 at the corresponding frequency, wherein
inter alia at certain points in time both oscillation exciters 37
exhibit the same length and inter alia at other points in time
exhibit the length ratios that are opposed to FIG. 7. This results
in an excitation of oscillating rotational movements of the tool
holder 6 around the axis of rotation extending through the point
P.sub.M, such that at the point P.sub.M an oscillating torsional
moment M is transmitted into the bonding tool 5. Thus the bonding
tool 5, as shown in FIG. 7, is excited to perform a torsional
oscillation. For comparison FIG. 7 also shows the tools
longitudinal axis W at the idle state with no applied voltage as it
is shown in FIG. 3. The center point of the rotational movement is
located on this reference line W, i.e. it represents a so-called
node of the eigenform. The tool tip 9 in contrast exhibits a
pronounced deflection perpendicular to the reference line, i.e. it
is located at a so-called antinode. In the course of the
oscillation cycles the tool tip 9 moves mainly perpendicular to the
tool axis W. While pressing an electrical conductor that is to be
bonded onto a substrate (not shown here) with a tool tip 9 the
conductor is also excited to oscillations relative to the substrate
thus creating a bond connection.
[0047] In the embodiments according to the invention shown in FIGS.
3 and 7 the voltage source 42 (which is not shown in FIG. 7) is
tuned to the entire oscillating system with respect to the
generated alternating voltage and its voltage frequency such that
with application of the alternating voltage the geometrical
deformation lines 49 of the two oscillation exciters 37, which
correspond to the main geometrical deformation lines 50 of the
piezo elements 38, extend perpendicular to the polarization
direction P of the piezo elements 38. The main geometrical
deformation lines 49, 50 correspond to the main direction of
deformation that is independent from the leading sign. In FIG. 7
the axis of rotation extending perpendicular to the drawing plane
through the point P.sub.M is marked with A and the torsional moment
transmitted into the bonding tool 5 with respect to this axis is
marked with the reference sign M.
[0048] FIG. 8 shows the discussed ultrasonic transducer 35 mainly
in a cross sectional side view in connection with an assembly frame
32 that has a different design compared to the one shown in FIG. 1.
It can be mounted preferably to the pulley 3 shown in FIG. 1 by
means of a screw connection 51 that is only indicated here, i.e. it
can be inserted into the bonding head shown in FIG. 1 instead of
the assembly frame 32 that is shown there. At the ends 52 of the
lower cross members that point to each other the assembly frame 32
is attached to each one piezo element holder 16. This attachment
may be done integral respectively as a single piece or with several
parts by any suitable means (e.g. through bonding, screw connection
and the like). In a preferred embodiment according to the invention
wherein the connections are done as a single piece at the locations
with reference numeral 52, the combination of the transducer body
15 and assembly frame 32 is a single component. Based on the
illustration shown in FIG. 8 the hatching in the area of the piezo
element holders 16 would then be chosen to be identical to the
hatching of the assembly frame 32. The connection in each case
takes place in a central longitudinal area of the oscillation
exciters 37 on the level of the material bridge 22, such that a
separate retaining fork 19 (compare FIG. 1) can be omitted. In the
lower cross member 53 paired sections 33 with reduced frame cross
section and that serve as solid state pivots are provided, each
adjoining to the ultrasonic transducer 35 and the vertical members
54. Thus a single piece transducer parallelogram is formed that
allows for a certain elastic lowering of the bonding tool 5 by
means of a downwards oriented contact force F. The contact force F
may be applied e.g. at the material bridge 22, as shown in FIG. 8,
or at other locations of the transducer.
[0049] In FIGS. 9 and 10a, 10b another preferred embodiment of an
Ultrasonic transducer 35 according to the invention is shown that
is different from the previous figures. For ease of presentation
with regard to according attributes the same reference signs and
numerals as above are used. In FIGS. 9 and 10 a bonding tool 5 is
inserted into the ultrasonic transducer 35, and attached in it
(compare also FIGS. 10a, 10b) by means of a clamp screw 8. The
ultrasonic transducer 35 comprises a transducer body 15, which is
apart from a bore 7 for the insertion of the bonding tool 5 and a
threaded bore to screw in the clamp screw, a rectangular cuboid
made from a single piece of material. In the shown example the
ultrasonic transducer 35 comprises a total of four oscillation
excitation elements 55, each one plate shaped piezo element 38. Two
of these piezo elements 38, are arranged one behind the other with
respect to the direction of the longitudinal axis of the tool W,
and bonded planar onto one side respectively onto the same surface
39 of the transducer body 15, wherein the piezo element 38 that is
facing the bonding tool 5 comprises an opening for the clamp screw
8. On the opposing surface 40 that is extending in parallel to
surface 39 two additional piezo elements 38 are bonded that are
aligned to the aforementioned piezo elements with respect to the
projection. In so far the transducer body 15 in the example of
FIGS. 9 and 10 comprises only one piezo element holder 16. FIG. 10b
shows schematically simplified that the ultrasonic transducer 35
with the attached bonding tool 5, exhibits an oscillation mode with
a waveform in the mounting point 56 of the bonding tool 5, at which
the clamping occurs, that causes a rotational oscillating movement
around an imaginary respectively geometrical axis of rotation A,
that extends through the node on the level of the mounting point 56
parallel to the drawing plane of FIG. 10b. In so far also an
imaginary respectively geometrical reference plane E in FIG. 10b
that is perpendicular to the drawing plane of FIG. 10b is spanned
by the longitudinal axis of the tool W (i.e. the longitudinal
direction of the tool) and said rotational axis A. It becomes
apparent that all four oscillation excitation elements 55 (i.e. all
piezo elements 38) are arranged sideways interspaced with respect
to reference plane E respectively in a direction perpendicular to
the extension plane of the piezo elements 38. FIG. 10a shows the
respective polarization directions P of these four piezo elements
38. On the left side with respect to the viewing direction the
upper piezo element 38 comprises a polarization direction P that
points away from the surface 39, whereas the lower piezo element 38
comprises a polarization direction P that points towards the
surface 39. On the opposing side the upper piezo element 38
comprises a polarization direction P that points towards the
surface 40 and the lower piezo element 38 comprises a polarization
direction P that points away from the surface 40. For the case that
the oscillation excitation element holder 57, that in this example
because of the use of piezo elements as oscillation exciters is the
piezo element carrier 16, is e.g. grounded and an alternating
voltage that is in phase is connected to the free surfaces of the
piezo elements 38, alternating elongations and contractions that
change in time, result within the planes of the piezo elements 38
and thus also or even mainly in parallel to the imaginary extension
of the longitudinal axis of the tool. The arrows shown in FIG. 10b
depict that the two piezo elements 38 with their polarization
direction P pointing to the transducer body 15 experience a length
change (at the depicted point in time an elongation) in phase to
each other and that the two other piezo elements 38 with a
polarization direction pointing away from the transducer body 15
also experience a length change (at the depicted point in time a
compression) in phase to each other, but in opposing direction with
respect to the aforementioned piezo elements 38. Thus the two piezo
elements 38 that are arranged aligned opposing each other with
respect to the reference plane E experience length changes opposed
to each other. Also each two piezo elements 38 bonded to the same
surface (39 or 40) experience length changes opposed to each other.
In FIGS. 9 and 10a, 10b the voltage supply respectively current
supply of the piezo elements 38 is not shown. As discussed above
the transducer body may be e.g. grounded (or connected to another
potential) and to the free surface of all piezo elements 38, e.g.
also by means of electrically conducting connections between them,
an alternating voltage in phase to each other may be applied.
[0050] The transducer body 15 is a basic cuboid body made from a
metallic material, with its longest side standing vertically i.e.
extending in the direction of the extension of the longitudinal
axis of the tool W. Because of the above described length changes
in opposite directions of the piezo elements 38, the transducer
body 15 performs a torsional oscillation, wherein the cross section
in "bending direction", i.e. in with respect to the viewing
direction of FIGS. 10a, 10b sideways respectively horizontal
direction, exhibits the smallest elongation. Preferably and in the
shown example the transducer body oscillates, as shown in FIG. 10b,
in its second torsional eigenmode. With two free edges this
eigenmode comprises three nodes, wherein the lowest is located at
the level of the mounting point 56 of the bonding tool 5. Below
that in this example three other nodes, also marked with reference
numerator 58, are distributed along the length of the bonding tool
5. Thus the bonding tool 5 also performs torsional modes. The
bonding tool 5 and the transducer body 15 are tuned with respect to
their geometrical dimensions and the material properties such that
each of them exhibits approximately the same eigenfrequency (for
the above mentioned eigenmodes). When these two components are
assembled together, the overall system also shows an according
eigenfrequency. Thereby it is preferred (as shown), that the upper
node 58 of the bonding tool 5 and the lower node 58 of the
transducer body 15 are located at the same point. At this same
location respectively on this level also the clamp of the bonding
tool 5 by means of the clamp screw 8 (in the example a set
screw).is located. Accordingly the bonding tool 5 carries forward
the torsional oscillation of the transducer body 15 almost
seamlessly. To be able to clamp the bonding tool 5, the bore 7 in
the form of a tapped blind hole for the bonding tool 5 is not
located exactly in the center of the flexural plane of the
transducer body 15, wherein however a small offset is affecting the
oscillation behavior only minimally. Alternatively a suspension of
the bonding tool in the ideal center of the flexural plane would be
possible. In the plane orthogonal to the flexural plane the bonding
tool 5 in the example is located in the ideal center.
[0051] In the exemplary embodiment (compare FIG. 9) the suspension
of the ultrasonic transducer 35 respectively its mounting to the
bonding head may be accomplished by means of two connecting devices
59 that are mounted opposing each other on the two surfaces on the
side of the transducer body that are orthogonal to surfaces 39, 40.
They each comprise a connecting bore 60 in or through which the not
depicted mounting screws for the mounting at the bonding head may
be routed to the bond head. Each connecting device comprises a
solid state pivot 61 (i.e. a total of four solid state pivots 61)
above and below the connecting bore 60, wherein these regions
exhibit a small cross section in order to de-couple the torsional
oscillations. Preferably these flexure zones are located exactly on
the level of the upper and the middle node 58 of the transducer
body 15 (compare FIG. 10b). Here the base body performs a quasi
pure rotation, whereby the pivot joints perform ideally and in this
way may de-couple the oscillation system from the environment.
Alternative variants are possible wherein the solid state pivots
are located on the level of the upper and lower node 58 of the
transducer body 15 or on the level of the middle and the lower node
58 of the transducer body 15. Above and below the solid state
pivots 61 connections of the connecting device 59 with the
transducer body 15 are located. Preferably these connecting devices
59 are made as a single piece respectively integrally, i.e. the
suspension and the base body are one piece, and other deviating
embodiments are also possible.
[0052] In the exemplary embodiments shown in FIGS. 9 and 10 the
ultrasonic oscillation are also produced by thin piezo plates. Also
here the oscillation direction that is orthogonal to the
polarization direction P and to the electrical field is utilized.
As described above in order to achieve the ideal excitation of the
oscillation mode of the base body (particularly the second flexural
mode), four piezo elements 38 are utilized, wherein the each
diagonally opposing elements synchronously perform elongations and
contractions that change in time. Variants are possible e.g.
thereby that either the piezo elements 38 that are bonded to the
two surfaces 39 or the piezo elements 38 that are bonded to the two
surfaces 40 are omitted. Also in the hereby generated embodiment
the transducer body 15 would be excited to a second torsional mode.
Another variant would be possible with the in respect to the FIGS.
10a, 10b if either the two upper or the two lower piezo elements 38
would be omitted. In such a configuration the transducer body 15
would be excited to its first torsional mode, such that also here
with suitable tuning an oscillating transmission of the torsional
moment into the bonding tool 5 occurs. Analogous also embodiments
are possible wherein based on the FIGS. 9 and 10 on each surface
39, 40 one or more additional piezo elements 38 are arranged one
behind the other in the direction of the extension of the
longitudinal axis of the tool W, to thereby excite the transducer
body 15 to higher torsional modes.
[0053] All embodiments and attributes disclosed herein are (for
themselves) essential for the invention. In the disclosure of the
application herewith also the disclosed content of the
according/enclosed priority documentation (copy of the provisional
application) is included with its full content, also for the
purpose to include attributes and embodiments from this document in
the claims of the present application.
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